At the heart of many computer systems is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the reading and writing functions.
The write head includes at least one coil, a write pole and one or more return poles. When current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic media, thereby recording a bit of data. The write field then travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
Magnetoresistive sensors such as a Giant Magnetoresistive (GMR) sensors, Tunnel Junction Magnetoresistive (TMR) sensors or a scissor type magnetoresistive sensors have been employed to read a magnetic signal from the magnetic media. Such a magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the magnetic media. The sensor is located between first and second magnetic shields and the spacing between the shields effects data density. A smaller spacing between the shields results in an increase in data density by increasing the number of bits that can be recorded and detected on a given length of data track.